Area Forecast Discussion
Issued by NWS Jackson, KY

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000 FXUS63 KJKL 271810 AAA AFDJKL AREA FORECAST DISCUSSION...UPDATED National Weather Service Jackson KY 210 PM EDT Sat May 27 2017 .UPDATE... Issued at 210 PM EDT SAT MAY 27 2017 Scattered convection has initiated along a remnant outflow boundary aligned from just north of KBWG to south of KEKQ. Convection is also popping up closer to the nearly stalled frontal boundary just north of the Ohio River. Have freshened up the POP trends through the rest of this afternoon. Expect a gradual uptick in activity, with a few cells pushing severe limits. Updates have been sent. UPDATE Issued at 1110 AM EDT SAT MAY 27 2017 The latest surface map reveals the quasi-stationary frontal zone still north of the Ohio River this morning. Some weakening outflow from previous convection that passed to our north during the pre- dawn hours, allowed for some isolated showers across portions of the area this morning. This boundary, when it was more evident from the radar, was aligned from near a line from Inez to Somerset. The latest satellite shows plenty of cloud cover back off towards central Kentucky, with some partial clearing moving in across western Kentucky out ahead of a weaker mid/upper level short wave trough. A complex of storms was gradually weakening across TN/KY, with only some widely scattered storms occurring along the leftover outflow. This short wave will move in across the area this afternoon, with some thinning of the clouds and some destabilization expected. As such, would expect some scattered to numerous development between 18 to 00z, with a few cells potentially approaching severe limits, as well as locally heavy rainers. This weak forcing will be exiting after 00z. Still expect a lull in convection, until late tonight into Sunday morning out ahead of the larger complex of storms to approach from the west. Tried to fine tune the POPs according to the latest mesoscale conditions, as well as input from the higher resolution model guidance. Updates have been sent. UPDATE Issued at 652 AM EDT SAT MAY 27 2017 Isolated showers have worked south to near the Mountain Parkway this morning. As expected, cap appears to be holding, so no real impact from the showers this morning. Temperatures have come up with the moisture advection, so have made some small tweaks to capture current trends. && .SHORT TERM...(Today through Sunday) Issued at 413 AM EDT SAT MAY 27 2017 An active weather pattern setting up to kick off this holiday weekend. The lower levels are moistening up this morning thanks to some southwest flow in the low levels advecting some moisture into the region. This has already set off a few isolated showers in the bluegrass region. This activity will likely expand through the daybreak hours with cloud heights coming down as moisture streams into the lower levels. We remain very capped this morning, so not expecting any storms to develop just yet. This all changes as a boundary just to our north settles south into northern Kentucky. Instability will build to the south of this boundary with over 2000J/kg of MLCAPE and LI`s around -8C. This is pretty good instability for our neck of the woods. Added convergence along the frontal zone in the north could help to spark some showers/storms as we head through the afternoon and early evening hours. With the front stretched out east to west and the mean flow coming from the west, will have to watch for potential some training storms. PW values will reach nearly 1.6 inches by this afternoon putting us very close to the 99th percentile for May. This all points towards the potential for heavy rainfall and flash flooding. Freezing level is also quite high supporting more warm rain processes. Thus, we have issued a flash flood watch for most of eastern Kentucky. There will also be a severe threat this afternoon with the good instability mentioned above. Shear is not the best in the northern portion of our area, but does get a bit better to the south. Regardless, instability may be enough to make up for the lack of shear and thus pose a damaging wind threat with any storms that develop. The weaker shear would probably limit the overall hail threat, although some small hail would be possible. Finally with outflow boundaries possible, this could help to escalate low level SRH and possibly lead to a low tornado threat. However, this will be highly conditional on storm evolution today, so will continue to downplay the overall tornado threat. Activity will likely diminish by late evening with a shortwave ridge pushing across the Ohio river valley. This will provide a lull overnight into early Sunday morning. The lull could be interrupted by any upstream convection that may try to work into the region from the west. This will be clearly determined by where convection forms and the overall steering pattern. At this point, CAMS all seem to support a more southerly track of any MCS tonight, likely missing our area, assuming the mid level ridge is strong enough. Then the focus shifts to Sunday as instability builds once more. 00z NAM really doesn`t bring the better instability in until late Sunday evening, suggesting we may see a later onset of stronger storm potential on Sunday. However, shear is stronger on Sunday, so whatever forms upstream and tracks into the area could have some damaging winds with it late Sunday. Hail doesn`t appear to be a great threat as storm initiation should take place upstream with the cold front with stuff turning more QLCS in nature by the time it reaches us. With the potential for additional rounds of showers, have put the flash flood watch out through Sunday evening. .LONG TERM...(Sunday night through Friday) Issued at 435 AM EDT SAT MAY 27 2017 Models remain in generally good agreement during the long term period. the period should begin with a ridge across the Gulf of Mexico with another ridge over the Western Conus. An upper level low should be over western Ontario to begin the period with an associated trough extending into the MS Valley to Arklatex region. At the surface, a triple point area low low pressure should move across the Southern Great Lakes and into Ontario and Quebec to begin the period with the trailing cold front moving across the area Sunday night into early on Monday. Through midweek, the region will remain under the influence of the upper low over southern Canada and the associated trough, the axis of which should move east of the area around midweek while the axis of the ridging in the western Conus moves to near the Continental Divide at midweek as an trough nears the West Coast. A shortwave should rotate into the Great Lakes Tuesday into Tuesday night around the upper level low. An associated surface low should move across the Great Lakes with the trialing cold front moving across the area on Tuesday into Tuesday night. The latest guidance from Wed night through the end of the period has the trough lifting on out to the north and east with general height rises across the OH Valley and Southern to Central Appalachians though west to northwest flow persists. The 0Z GFS and 0Z ECMWF are generally drier than their previous operational runs from Wed night into Thursday with stronger surface high pressure over the OH Valley. Pending disturbances in northwest flow and available moisture, a few showers or even a stray thunderstorm cannot be completely ruled out just yet during the Wed night to Thursday period and on into the end of the period. The most active portion of the period will be as the cold front moves through the area on Sunday evening. MUCAPE and SBCAPE should be in the 1000 j/kg to 2500 j/kg early in the period with bulk shear of about 40KT and mid level lapse rates of 7C to 8C, damaging winds and hail up to half dollar size would appear possible with any thunderstorms along or in advance of the cold front on Sunday evening as flow will generally be unidirectional. Locally heavy rain will also be a concern until the boundary moves through and deeper moisture departs. The highest pops were carried early in the period with isolated to scattered pops at times for the rest of the period with either the secondary front or disturbances in west northwest to northwest flow. Temperatures should average close to normals for late May. && .AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon) ISSUED AT 210 PM EDT SAT MAY 27 2017 MVFR stratocu will gradually mix out over the next hour or so. Scattered to numerous showers and thunderstorms will affect the area through 01z, before diminishing in coverage. Some of the storms may approach severe limits with winds of 40 to 50 kts potentially and temporary IFR or worse conditions. Given the isolated nature of these, have not included a mention in the TAFs. The next concern will be the potential of a larger complex thunderstorms affecting eastern Kentucky generally between 06 and 12z. The models have trended a bit farther southwest with the brunt of this complex. For now, have carried a period of showers and thunderstorms, with rain showers likely lingering into the mid- morning hours behind the main line of storms. && .JKL WATCHES/WARNINGS/ADVISORIES... Flash Flood Watch through late Sunday night for KYZ050>052- 058>060-068-069-079-080-083>088-104-106>120. && $$ UPDATE...GEOGERIAN SHORT TERM...KAS LONG TERM...JP AVIATION...GEOGERIAN is the U.S. government's official web portal to all federal, state and local government web resources and services.